1. Field of the Invention
The present invention relates to an ultrasonic contact transducer for point-focussing surface waves, which is applicable to the nondestructive testing technique of the surface or subsurface of a specimen to be tested, and more particularly, to an ultrasonic contact transducer for generating surface waves, focussing the waves at one point on the surface of the specimen and receiving again the signals scattered from the surface flaws or subsurface flaws of the specimen, in order to detect the surface cracks, surface flaws, subsurface flaws of the specimen and to detect the delamination in a thin laminated film.
2. Information Disclosure Statement
Conventionally, in the ultrasonic testing of materials, focussed radiators have been frequently used to increase the sound intensity and to improve the resolution. The focussing has been realized by means of either curved radiators or plane radiators with curved contact lenses. However, so far, focussing contact type ultrasonic transducers have been designed in order to examine the interior of a specimen. Although a kind of, angle beam ultrasonic transducers have been designed and used to generate surface acoustic waves, they are not focussed but dispersed with a wide beam width resulting in poor resolution.
It is the object of the present invention to provide an ultrasonic transducer with a narrow beam width and a high sound intensity at the focal point on the surface of the specimen thereby improving flaw detection of the surface of the specimen.
The present invention, uses a curved piezoelectric element and an acoustic contact lens which enables the rays of the surface waves, such as Rayleigh waves, creeping longitudinal waves and horizontal shear surface waves, to be focussed at one point on the surface of the specimen to enhance flaw detection.
The narrow beam width at focal distance improves lateral resolution and more effectively sizes and images the surface flaws and subsurface flaws of the specimen relative to conventional angle beam transducers. Also, the high sound intensity at the focal distance enables the examination of the farther zone of the specimen possible. Furthermore, if creeping longitudinal waves are used, the transducer makes the examination of the dead zone in a specimen with an L or T type structure possible.
For further discussion of the present invention, see Kim et al, "Development of Surface Point-Focussing Ultrasonic Transducer Using PVDF", IEEE 1989 ULTRASONICS SYMPOSIUM PROCEEDINGS, PP. 609-612 B. R. MCAVOY. VOL 1, Nov. 16, 1989, and IEEE 1989 Ultrasonics Symposium and Short Courses, Program and Abstracts, page 163, Legrand Hotel, Montreal, Quebec, Canada, Oct. 3-6, 1989, both of which are incorporated herein by reference as if fully set forth hereat.
The preceding objects should be construed as merely presenting a few of the more pertinent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to both the summary of the invention and the detailed description, below, which describe the preferred embodiment in addition to the scope of the invention defined by the claims considered in conjunction with the accompanying drawings.